‡¹ In antique Latin, by words ending in ius or ium the ius/ium became ī in genitive singular. E.g. in antique times, fīlius became fīlī (later and nowdays fīliī) and negōtium became negōtī (later and nowadays negōtiī) in genitive singular.

The singular vocative of second declension -us nouns is the only place in pure Latin words in which the vocative ever differs from the nominative forms: -e instead of -us. The plural vocative is the same as the nominative. As seen in filius, filiī, the vocative singular changes the -ius into an -ī, instead of changing the -us into an -e.